ST eFuse (electronic fuse) User guide

Brand: ST

Model: eFuse (electronic fuse)

Type: User guide

Order code: BR2201EFUSEQR

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GLOSSARY AND DEVELEOPMENT TOOLS

DEMOBOARDS

Accuracy – the maximum deviation from the specied over voltage, and over current protection levels.

Auto-retry – an auto-retrying device will turn itself back on after a thermal shutdown once the die temperature is below the

hysteresis value.

Bias current – the current needed by the eFuse itself to maintain operation.

Overload current limit, or current limit trip-point – the eFuse reacts to overcurrent events by reducing the conductivity of the

pass element once the current exceeds this limit.

Short circuit current – when a strong overload occurs and the output voltage drops as a consequence, the device limits the

current to a level below the regular current limit.

dV/dT – this refers to the internal circuitry that controls the output voltage rise at turn-on. The external dV/dT pin allows the

user to adjust the soft-start time.

Enable-fault – the enable-fault pin is a dual-function pin: it lets the user enable and disable the device, and at the same time

provides the device status through a three-state logic.

Gate driver – to protect the supply and pass element, STEF01 and STEF12S include an internal charge pump to drive an

external MOSFET that prevents reverse currents and large transient voltages which may occur during high-current limiting.

Hysteresis – to prevent an auto-retrying device from repeatedly turning ON and OFF after a thermal shutdown, the device only

turns back on once the temperature has dropped by the hysteretic value.

Latch – when a thermal fault occurs, the device will remain OFF until the power or enable-signal is cycled by the user.

Output Voltage Clamp – if the input voltage exceeds the pre-dened voltage clamp value, the internal protection circuit

ensures the output voltage does not rise above this preset value.

Pass element – the voltage and current pass through a low-resistive power MOSFET which can be controlled to limit the

output current and voltage in reaction to fault conditions.

Power dissipation – during normal operation, the power dissipated by the device depends on the pass element’s RDS(on) and

the load current. When voltage/current is regulated, which happens during start-up and in case of faults, the excess power is

dissipated in the form of heat. In persistent faulty conditions, this heat shuts the device down as a consequence of thermal

protection.Thermal design and correct soft-start congurations are important to prevent unwanted shutdowns, which are most

likely to occur during start-up phases or in high and continuous current conditions.

Power Good (PG) – a signal to indicate that the output voltage is very close to the input and that no current/voltage limitation

is in place. It can be used for power-sequencing, reset-triggering, and more.

Soft Start (SS) – a Soft Start is a controlled delivery of the output power , which minimizes inrush currents, thus protecting the

power supply from overloading. The Soft Start time can be extended by adding a capacitor to the dV/dT pin.

Thermal shutdown – during a persistent fault, the eFuse die will heat up. Once the shutdown temperature (typically 175°C) is

reached, the device will turn off the internal pass element and go in latch or auto-retry state.

UVLO (Undervoltage lockout) – the UVLO makes sure the device does not turn on until the supply voltage is high enough, thus

contributing to the eFuse’s predictable and reliable performance.

For more information, visit us on www.st.com/efuse

Part number Product Description

STEVAL-EFUSE01 STEF01 Evaluation board based on the STEF01 fully programmable universal electronic fuse

STEVAL-IFP021V1 STEF12/STEF05 5 V and 12 V power line protection based on STEF05 and STEF12 electronic fuses

eFuse (electronic fuse)

Quick reference guide

eFuses PORTFOLIO OVERVIEW

HOW DOES AN eFuse WORK ?

KEY FEATURES

PACKAGE RANGE

Ensuring safer designs and more efﬁcient applications

An eFuse is a low-resistance switch connected in series to the main

power rail and controlled by logic circuitry to protect loads and power

supplies. Smaller, faster and more efcient than conventional fuses

or polymeric PTCs, eFuses detect and react to overcurrent and

overvoltage conditions, and do not require replacement after a fault

event.

Quick and intelligent response to faults

Unlike conventional fuses, which are based on the principle that a conductor will overheat and melt during an overload

condition, the eFuse only clamps the output voltage and/or limits the throughput current, thus allowing the device to be

supplied correctly, before eventually disconnecting the load in case of persistent failure. This prevents load and supply

damage from occurring and avoids false triggering caused by transient conditions. Moreover, in applications powered by DC

buses, eFuses reduce the bus droop due to faulty loads, avoiding the propagation of nuisance or undervoltage to other loads

connected to the same bus.

Reduced maintenance

Since eFuses do not sacrice their pass element, they can immediately be reset with a signal from the system by either cycling

the supply power or by simply waiting, if auto-retry is used. The equipment’s uptime is maximized and the cost and complexity

of maintenance are reduced.

Inrush current control

Inrush current conditions can occur during start-up or hot-plugging. eFuses ramp the output voltage up in a controlled manner

to prevent large inrush currents from overloading the power supply. This feature is crucial when multiple loads are supplied by

a single power supply.

Flexible application design

Every eFuse can be programmed and tailored to your specic needs. Most eFuses allow users to set the current limit and

start-up time. The undervoltage lockout and output clamp levels as well as the device’s operating mode (latch-off or auto-retry

mode) can also be congured on certain part numbers.

When an overload or short-circuit condition occurs, the eFuse limits the current to a pre-dened safe value. When an

overvoltage condition occurs, the eFuse clamps the output voltage to a safe level,thus protecting the load from abnormalities

caused by malfunctioning power supplies.

The eFuse disconnects the load from the power supply if fault conditions are persistent. Depending on the version, the device

operates either in latch-off mode, which means it is switched-off and must be re-armed manually, or in auto-retry mode

where the device will automatically re-start.

Output voltage clamping

Each eFuse has a predened maximum output voltage safe value.

If the input voltage exceeds this value, the eFuse clamps the output

voltage to the preset value and allows the device to operate without

damaging the load or system.If the overvoltage is persistent, the eFuse

disconnects the load.Most eFuses have a pre-set voltage clamp value.

The STEF01 allows users to congure it.

Current limiting

When an overload condition occurs, the eFuse reduces the

conductivity of the internal pass element to effectively limit the

current to a precongured value. If a strong overload or short circuit

occurs, the device enters the foldback current limit, and eventually

disconnects the load, thus protecting the power supply. This value is

usually congured using an external resistor.

Undervoltage lockout

The undervoltage lockout feature disconnects the load from the

supply if the input voltage is lower than a preset minimum. By avoiding

issues caused by too low supply voltage such as wrong voltages from

bandgap references, incorrect control signals in logical circuitry, and

transistors being only partially ON or OFF, the undervoltage lockout

increases system predictability.The STEF01 allows users to set the

undervoltage lockout threshold between 8 V and 45 V.

12 V, 60 A High precision eFuse with 0.85 mW RDSON current and

temperature monitor pins. Parallel conguration.

QFN 32 5x5 package

12 V, 4 A high-precision simple eFuse

TSOT23-8L and DFN 3x3 packages

5 V, 4 A high-precision simple eFuse

TSOT23-8L package

5 V + 12V in one 3 A eFuse

TSOT23-8L package

5 V + 12 V in one 3 A eFuse with current monitor

QFN 2x3 package

5 V + 12 V in one 3 A eFuse with reverse current protection

on 5V channel

DFN 2x3 package

8 – 48 V, 4 – 5 A Fully programmable eFuse with 30 mW RDSON

HTSSOP14 package

Turn-on delay/Soft start

The eFuse provides a dened and predictable ramp-up of the output

voltage during start-up, to ensure the inrush current is maintained

within safe connes and protects both the load and the power

supply.The soft start duration can be easily congured by an external

capacitor.

Enable/Fault pin

All eFuses feature an enable/disable pin, to turn-on/off the device. In addition, some products offer the

enable/fault pin, which is a dual-function pin that allows users to manually turn the output off and to read

the current state of the device. The eFuse can be reset by toggling this pin after a thermal shutdown.

The pin can be used as a regular enabling pin and can be connected to a monitoring circuit to notify

thermal shutdown events. It can also be connected to the Enable/Fault pins of other eFuses, to achieve a

simultaneous Enable/Disable operation for all devices.

VOUT / Source

R-lim

I-limit

dV / dT

IN EN / Fault

OUT

STEF12

COUT

VCC

LOAD

Controller

CIN

Control &

Protections

KEY BENEFITS OF ELECTRONIC FUSES

High Power

• SERVER

• TLC infrastructures

• Industrial controls

• NAS/SAN

•

Low Power

• Data-storage

• Industrial

• Consumer

12 V

48 V

Transient voltage

Output voltage

Voltage clamp level

Short limit

Load current

Trip point

Input voltage

Lockout threshold

Output voltage

Enable signal

Input voltage

STEF01

STEF12S

STEF05S

STEF512GR

STEF512SR

STEF512PUR

STEF12H60M

12 V

5 V

Dual

3.3

1.5 3 4 5 7 24 60

Power Breaker Standard eFuses Dual rail 5 V + 12 V Fully programmable 3,3 V or 5 V rail

Low side timed switch High power eFuse

High power load switch

Continuous current (A)

(Not to scale)

Typical voltage rail (V)

(Not to scale)

Legend:

STEF033

STEF12S STEF12H60M

STEF05S

STEF05

STEF05D

STEF05L

STEF512GR

STEF512PUR

STEF512SR

STEF4S

STEF01

STEC01

(Safety IC)

STEL12H24

STPW12 STEF12

STEF12E

DFN 2x3 10L QFN 2x3 10L DFN10 3x3

HTSSOP14 QFN 32 TSOT23-8L

ST eFuse (electronic fuse) User guide

ST eFuse (electronic fuse) User guide

ST eFuse (electronic fuse) User guide

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